<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Title</title>
        <style>
            *{
                padding:0px;
                margin:0px;
            }
            .container{
                width:400px;
                height: 500px;
                border:1px solid red;
            }
            .d1,.d2,.d3{
                width:300px;
                height: 200px;
                border:1px solid blue;
            }
            .d3{

                /*相对定位是参考自己原来的位置进行偏移的*/
                position: relative;
                top:0px;
                left:0px;
            }
        </style>
    </head>
    <body>
        <div class="container">
            <div class="d1"></div>
            <div class="d2"></div>
            <div class="d3"></div>
        </div>
    </body>
</html>